Low-viscosity ester mixtures

ABSTRACT

The invention relates to the preparation of low-viscosity ester mixtures for transesterification of vegetable or animal fats or oils with monofunctional esters.

RELATED APPLICATIONS

This application claims benefit to European Patent Application No.07019768.6, filed Oct. 10, 2007, which is incorporated herein byreference in its entirety for all useful purposes.

BACKGROUND OF THE INVENTION

The invention relates to the preparation of low-viscosity ester mixturesby transesterification of vegetable or animal fats or oils withmonofunctional esters. The randomized transesterification of varioustriglycerides with one another, catalyzed with bases, acids or enzymes,is known and is described in Journal of the American Oil Chemists'Society (1953) 30, 320-325; Biotechnology and Bioengineering (2006) 94(5), 877-887; Grasas y Aceites (2005) 56 (4), 267-275; Journal of FoodScience (2005) 70 (6), C365-C372; JP 11225671; Fett/Lipid (1998) 98 (2),60-65; Journal of Industrial and Engineering Chemistry (1948) 40,1183-1190. This transesterification in turn leads to triglycerideshaving a comparably high viscosity and high solidification point. Theyare therefore not suitable, for example, as an auxiliary or additive orsolvent for finishes.

Esters having low viscosity and low solidification point can be obtainedby transesterification of triglycerides with monoalcohols to give fattyacid alkyl esters and glycerol. This procedure is also well known and isdescribed in Bioresource Technology (2006) 98 (3), 639-647; Industrial &Engineering Chemistry Research (2005) 44 (25), 9535-9541; ChemicalEngineering & Technology (1999) 22 (1), 70-75. A disadvantage of theseprocesses is that glycerol forms as inevitable product which has to beseparated off since, particularly when used as a solvent or additive infinishes, free OH groups are as a rule problematic owing to theirreactivity, for example towards isocyanate groups.

Furthermore, the transesterification of triglycerides with carboxylicacids is known and is described in Tluszcze Jadalne (2002) 37 (1/2),82-92. In this approach, the fatty acids eliminated have to be separatedoff after transesterification is complete, in order to obtain estermixtures which can be used as solvents or diluents in coatingtechnology.

Starting from the process described in the prior art, it is thereforethe object of the present invention to provide a process, which is astechnically simple as possible, for the preparation of esters or estermixtures which are liquid at 23° C. with a viscosity of <50 mPa·s andhave a solidification point of less than −10° C., and removal ofcompounds containing hydroxyl and/or carboxyl groups is dispensed with.

EMBODIMENTS OF THE INVENTION

An embodiment of the present invention is a process for preparing estermixtures comprising reacting triglycerides with alkyl or cycloalkylesters of aliphatic or cycloaliphatic monocarboxylic acids.

Another embodiment of the present invention is the above process,wherein said triglycerides are triesters of glycerol with C6- toC22-carboxylic acids.

Another embodiment of the present invention is the above process,wherein said triesters of glycerol are free of OH groups and have 6 orless olefinic double bonds.

Another embodiment of the present invention is the above process,wherein said alkyl or cycloalkyl esters are free of OH groups.

Another embodiment of the present invention is the above process,wherein said alkyl or cycloalkyl esters are linear or branched alkylesters of monofunctional aliphatic carboxylic acids.

Another embodiment of the present invention is the above process,wherein said alkyl or cycloalkyl estersare butyl acetate, ethylpropionate, or mixtures thereof.

Another embodiment of the present invention is the above process,wherein said process is carried out in the presence of at least onecatalyst.

Yet another embodiment of the present invention is an ester mixtureprepared by the above process.

Another embodiment of the present invention is the above ester mixture,wherein said ester mixture have shear viscosities of 12 to 50 mPa·s at23° C. and solidification points below 0° C.

Yet another embodiment of the present invention is a solvent comprisingthe above ester mixture.

Yet another embodiment of the present invention is a auxiliarycomprising the above ester mixture.

Yet another embodiment of the present invention is a process agentcomprising the ester mixture.

Yet another embodiment of the present invention is a fuel for internalcombustion engines comprising the above ester mixture.

Another embodiment of the present invention is the above solvent,wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at23° C. and solidification points below 0° C.

Another embodiment of the present invention is the above auxiliary,wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at23° C. and solidification points below 0° C.

Another embodiment of the present invention is the above process agent,wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at23° C. and solidification points below 0° C.

Another embodiment of the present invention is the above fuel forinternal combustion engines, wherein said ester mixture has a shearviscosity of 12 to 50 mPa·s at 23° C. and solidification points below 0°C.

DESCRIPTION OF THE INVENTION

It has now been found that the transesterification of triglycerides withalkyl esters of aliphatic or cycloaliphatic carboxylic acids is possibleand ester mixtures having the desired properties can be obtainedthereby. It is particularly advantageous that neither OH-norCOOH-functional cleavage products are obtained, the removal of whichwill be necessary in particular for the field of use of additives forfinishes.

The invention therefore relates to a process for the preparation ofester mixtures and the ester mixtures themselves thus obtainable, inwhich triglycerides are reacted with alkyl or cycloalkyl esters ofaliphatic or cycloaliphatic monocarboxylic acids.

In the context of the invention, triglycerides are fats and oils ofvegetable, animal and/or synthetic origin, preferably vegetable origin.

Preferred triglycerides are the triesters of glycerol with C6- toC22-carboxylic acids. Preferred triesters of glycerol of theabovementioned type have no free OH groups and furthermore have 6 orless, preferably 3 or less, olefinic double bonds.

Triglycerides of vegetable origin are, for example, palm oil, coconutoil, olive oil, rapeseed oil and oils of other seeds of cruciferousplants (carmelina, sea kale, turnip rape, mustard), sunflower oil, cornoil, cottonseed oil, peanut oil, hazelnut oil, poppy seed oil, linseedoil, safflower oil, thistle oil, coclebur oil, wood oil, soya oil andthe oils of other seeds of papilionaceous plants (lupins, caragana),hemp oil, marigold oil, Iberian dragon's head oil, evening primrose oil,coriander oil, black cumin oil, jatropha oil, castor oil or physic nutoil. Preferred oils of vegetable origin are rapeseed oil, sunflower oil,palm oil and soya oil.

Triglycerides of animal origin are, for example, butter fats, lards,tallows, blubbers, fish oils or fish liver oils.

In principle, said triglycerides may be used in the process according tothe invention individually or as any desired mixtures with one another.

The alkyl or cycloalkyl esters of aliphatic or cycloaliphaticmonocarboxylic acids may also contain heteroatoms, such as oxygen in theform of ether groups, in the alkyl or cycloalkyl radical. Any desiredmixtures of the alkyl or cycloalkyl esters may also be used.

The alkyl or cycloalkyl esters used for the transesterification arepreferably free of OH groups.

Linear or branched alkyl esters of monofunctional aliphatic carboxylicacids are particularly preferably used.

These preferably have 1 to 10, particularly preferably 2 to 8, carbonatoms in the alkyl radical.

Preferably, the aliphatic carboxylic acids of the linear or branchedalkyl esters of monofunctional aliphatic carboxylic acids have 1 to 10,preferably 2 to 8, carbon atoms.

In a preferred embodiment, the linear or branched alkyl esters ofmonofunctional aliphatic carboxylic acids are chosen so that the numberof carbon atoms therein is at least 4.

Examples of linear or branched alkyl esters of monofunctional aliphaticcarboxylic acids are n-butyl, isobutyl, 2-butyl, amyl, isoamyl,ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexylformate,

n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl,methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or2-ethylhexyl acetate,

ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl,methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or2-ethylhexyl propionate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl,isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexylor 2-ethylhexyl butyrate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl,isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexylor 2-ethylhexyl isobutyrate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl,isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexylor 2-ethylhexyl valerate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl,isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexylor 2-ethylhexyl pivalate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl,isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexylor 2-ethylhexyl capronate and

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl,isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexylor 2-ethylhexyl ethylhexanoate.

Monoesters of the abovementioned type based on acetic acid or propionicacid are particularly preferred.

Butyl acetate and ethyl propionate are very particularly preferred, italso being possible to use any desired mixtures thereof.

The weight ratio of the triglycerides used to the monofunctional estersused is in general from 0.1 to 10, preferably from 0.1 to 3,particularly preferably from 0.5 to 2.

The reaction is preferably carried out in the presence of at least onecatalyst, amounts of catalyst of 0.00001 to 0.3 part by weight, based onthe mixture of triglyceride and monoester, being preferred.

The amount of catalyst is particularly preferably 0.00001 to 0.02 partby weight. If enzymes are used as catalysts, the amount is 0.001 to 0. 1part by weight.

Catalysts in the context of the invention are, for example, alkali metalor alkaline earth metal carbonates, oxides, hydroxides or alcoholates,bismuth, tin, zinc, titanium, cobalt, iron, antimony or zirconiumcompounds, amidines, such as DBU or DBN, guanidines, such as tetra- orpentamethylguanidine, or amines, such as DABCO, the non-amine catalystsbeing preferred. The basic catalysts can be deactivated after thereaction by addition of acids, such as p-toluenesulphonic acid, ordibutyl phosphate. Catalysis by Bronsted acids is also possible but notpreferred.

Enzymes in the context of the invention are lipases, but the chemicalcatalysts are preferred.

In principle, C1 to C18-alcohols may also be added in addition to themonoesters for the transesterification.

Examples of such alcohols are methanol, ethanol, isopropanol,n-propanol, n-butanol, sec-butanol, diols, such as, for example ethyleneglycol, diethylene glycol, triols and tetraols, such as, for example,glycerol, trimethylolpropane, pentaerythritol and/or mono- ordiglycerides. Based on the amount of the monoester, such alcohols arehowever preferably used at most in amounts of 25% by weight.Particularly preferably, the addition of such alcohols is dispensedwith.

In a preferred embodiment, the triglycerides are reacted together withmonoesters and catalysts until a chemical equilibrium has beenestablished.

The reaction temperature during the reaction is preferably 160 to 260°C.

Furthermore, antioxidants, such as hydroquinone, hydroquinone monoalkylether or sterically hindered phenols, can be added to the reactionmixture, generally in amounts of 0.01 to 0.5% by weight, based on thereaction mixture.

Optionally, monoester used in excess can remain in the ester mixtureobtained after the process according to the invention or can beseparated off.

After the unconverted monoester has been separated off, the estermixtures preferably have shear viscosities of 12 to 50 mPa·s,particularly preferably 18 to 40 mPa·s, at 23° C.

After the unconverted monoester has been separated off, the estermixtures preferably have solidification points below 0° C., particularlypreferably −40 to −10° C.

The present invention furthermore relates to the ester mixturesobtainable by the present process and the use thereof as solvents,auxiliaries or process agents for coating materials, finishes, paints,adhesives, laminating materials, sealing materials, printing inks, inks,colorants, dyes, mordants, corrosion inhibitors and rust inhibitors,impregnating agents and graphic materials, as auxiliaries, plasticizers,levelling agents, reactive diluents, additives, in cosmetics or ascosmetic raw material, for the preparation of pharmaceuticalformulations, as lubricants, anti-friction agents, release agents orcoolants, as oil, in sunscreen agents, in or as diluents, cleaningagents or pretreatment agents, in foods of all types.

A likewise possible use of the ester mixtures obtainable according tothe invention is the use as fuel or as an additive in fuels for internalcombustion engines or as the oil phase of an oil-in-water emulsion whichis used as a cooling lubricant in metal processing.

For the abovementioned fields of use, it is firstly unimportant whetheror not the ester mixture still contains residual amounts of monoesterused for the transesterification. It is preferable to separate off themonoester used for the transesterification after the end of thetransesterification reaction.

If the ester mixtures according to the invention are used as fuel or asan additive in fuels for internal combustion engines, additives such ascetane number improvers, antioxidants, antifoams, corrosion inhibitors,flow improvers, surfactants or smoke reducers, can be added.

EXAMPLES

The determination of solids was effected by weighing on a dial balancefrom Mettler-Toledo at 125° C. to constant weight.

The GPC analysis (gel permeation chromatography) was recorded with THFas eluent. The evaluation was effected by determination of the peak areapercentages.

The viscosity determination was effected using a cone-and-plateviscometer from Anton-Parr at 23° C. The viscosities are stated in theunit [mPa·s].

General Preparation Method

The mixture of 2000 g of soya oil, 1000 g of monofunctional ester, 1 gof dibutyltin oxide and 2 g of hydroquinone was heated in an autoclaveunder autogenous pressure for 16 hours to 200° C. The viscosity of thereaction mixture was measured before the reaction, after the reactionand after the removal of the unreacted ester of the formula I bydistillation (in mPa·s). Furthermore, the solids content was measured bymeans of a dial balance at 125° C. after the reaction and after theremoval of the unreacted ester of the formula I by distillation (in %).The composition of the reaction mixture was determined after thereaction by GPC (proportion of triglyceride, diglyceride monoalkanoate,monoglyderide dialkanoate and alkyl fatty acid ester in % by weight),the unreacted ester of the formula I not being detected by the method.

In all examples, the pour points of the reaction mixtures were −10° C.before the reaction and −30° C. after the reaction (measured by coolingin a refrigeration bath and occurrence of the first precipitate). Dryice in acetone was used as the refrigeration bath. The temperature atwhich the precipitate formed in a test tube filled with 3 g of thesample was visually assessed.

The viscosity of the soya oil before the reaction was 57 mPa·s.

Example 1 2 3 4 Ester of the formula I butyl ethyl ethyl methoxyethylacetate butyrate propionate acetate Viscosity before the 3 2 7 9reaction Viscosity after the 8 5 6 12 reaction Viscosity after 28 37 3120 distillation Solids content determined Solids after reaction 72.868.5 71.1 72.3 Solids after distillation 97.5 99.5 98.9 96.4 Proportionsin % (according to GPC analysis): Triglyceride 38 68 55 45 Diglyceride32 20 27 29 monoalkanoate Monoglyceride 4 3 4 5 dialkanoate Alkyl fattyacid ester 23 7 13 19

In a further experiment, the mixture of 8000 g of soya oil, 4000 g ofbutyl acetate, 4 g of dibutyltin oxide and 8 g of hydroquinone washeated in an autoclave under autogenous pressure for 16 hours to 240° C.The viscosity of the reaction mixture was measured after the reactionand after the removal of the unreacted ester of the formula I bydistillation (in mPa·s). It was found that the viscosity after thereaction but before the distillation was 12.8 mPa·s. After removal ofthe butyl acetate, a viscosity of 20.8 mPa·s was found (solids content99%).

From the experiments, it is evident that the reaction according to theinvention results in a randomized transesterification which leads toester mixtures having advantageous properties (low viscosity incombination with low pour point).

All the references described above are incorporated by reference in itsentirety for all useful purposes.

While there is shown and described certain specific structures embodyingthe invention, it will be manifest to those skilled in the art thatvarious modifications and rearrangements of the parts may be madewithout departing from the spirit and scope of the underlying inventiveconcept and that the same is not limited to the particular forms hereinshown and described.

1. A process for preparing ester mixtures comprising reactingtriglycerides with alkyl or cycloalkyl esters of aliphatic orcycloaliphatic monocarboxylic acids.
 2. The process of claim 1, whereinsaid triglycerides are triesters of glycerol with C6- to C22-carboxylicacids.
 3. The process of claim 2, wherein said triesters of glycerol arefree of OH groups and have 6 or less olefinic double bonds.
 4. Theprocess of claim 1, wherein said alkyl or cycloalkyl esters are free ofOH groups.
 5. The process of claim 1, wherein said alkyl or cycloalkylesters are linear or branched alkyl esters of monofunctional aliphaticcarboxylic acids.
 6. The process of claim 1, wherein said alkyl orcycloalkyl esters are butyl acetate, ethyl propionate, or mixturesthereof.
 7. The process of claim 1, wherein said process is carried outin the presence of at least one catalyst.
 8. An ester mixture preparedby the process of claim
 2. 9. The ester mixture of claim 8, wherein saidester mixture has a shear viscosity of 12 to 50 mPa·s at 23° C. andsolidification points below 0° C.
 10. A solvent comprising the estermixture of claim
 8. 11. An auxiliary comprising the ester mixture ofclaim
 8. 12. A process agent comprising the ester mixture of claim 8.13. A fuel for internal combustion engines comprising the ester mixtureof claim
 8. 14. A solvent comprising the ester mixture of claim
 9. 15.An auxiliary comprising the ester mixture of claim
 9. 16. A processagent comprising the ester mixture of claim
 9. 17. A fuel for internalcombustion engines comprising the ester mixture of claim 9.